Water-borne, water redispersible, laminating adhesives for nonwoven applications

ABSTRACT

A specific class of water-borne, water redispersible laminating adhesives is disclosed which is desirable for bonding nonwoven substrates to themselves or to other substrates. The adhesives provide improved bond strength and improved water redispersibility when compared to laminating adhesives currently used for the same purpose. Furthermore, the novel adhesives are much less sensitive to the presence of significant levels of plasticizer than are laminating adhesives currently used, which exhibit reduced water redispersibility when such plasticizers are present in significant amounts. The novel laminating adhesives contain an aqueous styrene/acrylic polymer dispersion prepared by radical-initiated emulsion polymerization of unsaturated monomers in the presence of starch degradation products having a weight average molecular weight range of from about 2500 to 25000 and which are obtainable by hydrolysis in the aqueous phase. The adhesives may contain only the starch-modified, styrene/acrylic polymer dispersion, or may further include other components, such as plasticizers and/or rheology modifiers, when required. The novel adhesives are particularly useful in disposable articles wherein a nonwoven substrate is bonded to a second substrate via a water-borne, laminating adhesive. The disposable articles may include an absorbent core portion disposed between and proximate the nonwoven and second substrate.

FIELD OF THE INVENTION

This invention relates to novel water-borne, water-redispersiblelaminating adhesives which are used in articles wherein nonwovensubstrates are bonded to a second substrate, to processes for bondingnonwoven substrates and to articles comprising the novel laminatingadhesives.

BACKGROUND OF THE INVENTION

A nonwoven fabric is defined as an interlocking polymer networkcharacterized by flexibility, porosity and integrity. The individualfibers used to compose the nonwoven fabric may be synthetic, naturallyoccurring, or a combination of the two. The individual fibers may bemechanically, chemically, or thermally bonded to each other. Nonwovensare used commercially for a variety of applications including disposablearticles such as household wipes, surgical drapes, medical dressings,diapers, adult incontinent products and sanitary napkins. Tissue paperis a material closely related to nonwoven fabric in which the individualfibers may or may not be chemically bonded to one another. As usedherein, nonwoven fabric and nonwoven may be used interchangeably and areintended to include such tissue paper.

In the aforementioned applications it is necessary to adhere thenonwoven substrate to a second substrate. The second substrate may beanother nonwoven of a natural or synthetic polymeric substrate, such asa cellulosic, polyester or polyolefin. A commonly employed technique tobond the substrates together is the use of a water-borne, redispersiblelaminating adhesive. Suitable laminating adhesives must possess adequateadhesion to the substrates involved. For nonwoven applications they mustalso possess good flexibility, no staining or bleed through, suitableviscosity, and bonding range in order to function on commerciallyavailable equipment.

A variety of nonwoven applications have been developed which requirethat the water-borne laminating adhesive demonstrate appreciable watersolubility, redispersibility or sensitivity. In these situations thewater-borne laminating adhesive must provide a durable bond between thenonwoven substrate and the second substrate until exposed to apredetermined condition (e.g., water), after which the adhesive wouldrelease from the substrate(s). This water releasability is aparticularly desirable property in the disposable market whereflushability and/or degradeability are becoming critical.

Heretofore, the adhesive of choice in such disposable applicationscomprised homopolymers and copolymers of vinyl acetate prepared in thepresence of hydrolyzed polyvinyl alcohol. However, such polymers requirethe formulation of additional polyvinyl alcohol into the adhesivecompositions to impart the desired water sensitivity/redispersibility tothe adhesive. Furthermore, the inclusion of significant amounts ofplasticizer in adhesive formulations containing such polymers tends todecrease the water redispersibility of the adhesive, especially atelevated temperatures. In applications requiring such plasticizers, thispresents problems and limitations in formulating adhesives which possessboth required flexibility and water redispersibility. It would bedesirable, then, to develop a water-borne laminating adhesive for use insuch nonwoven applications which exhibits both improved adhesion andwater redispersibility over adhesives known heretofore, while at thesame time providing the formulator of the adhesive with the addedflexibility of utilizing plasticizers where required.

SUMMARY OF THE INVENTION

It has now been discovered that a specific class of water-borne, waterredispersible laminating adhesives is desirable for bonding nonwovensubstrates to other substrates. The adhesives provide improved bondstrength and improved water redispersibility when compared to vinylacetate-based, water-borne laminating adhesives currently used for thesame purpose. Furthermore, the novel adhesives are much less sensitiveto the presence of significant levels of plasticizer than are laminatingadhesives currently used, which exhibit reduced water redispersibilitywhen such plasticizers are present in significant amounts. Finally, thenovel laminating adhesives of the present invention do not requirepost-polymerization addition of components such as polyvinyl alcohol toachieve desired water redispersibility.

The novel laminating adhesives comprise an aqueous polymer dispersionprepared by radical-initiated emulsion polymerization of unsaturatedmonomers in the presence of starch degradation products having a weightaverage molecular weight range of from about 2500 to 25000 and which areobtainable by hydrolysis in the aqueous phase. The adhesives may consistonly of the starch-modified polymer dispersion, or may further compriseother components, such as plasticizers and/or rheology modifiers, whenrequired.

The novel adhesives are particularly useful in disposable articleswherein a nonwoven substrate is bonded to a second substrate via awater-borne laminating adhesive. The disposable articles may include anabsorbent core portion, wherein the inventive adhesives may be used as afixative to adhere particulate absorbent material together.

DETAILED DESCRIPTION OF THE INVENTION

The adhesives of the present invention are characterized by theirability to provide a durable bond between a nonwoven substrate and asecond substrate and otherwise meet the unique requirements of theapplication, including dry film flexibility, non-staining, machinableviscosity and later release upon exposure to water after a desiredresidence period, i.e., water redispersibility.

The adhesives comprise an aqueous polymer dispersion obtainable byfree-radical emulsion polymerization of unsaturated monomers, whichcontains at least one added starch-degradation product which isobtainable by hydrolysis in the aqueous phase and which has a weightaverage molecular weight (M_(w)) of from 2500 to 25000. Suchstarch-degradation products are referred to herein as sugared starches,as opposed to roast dextrins. The aqueous polymer dispersions utilizedin the adhesive compositions of the present invention and methods formaking the same are discussed in detail in Canadian Patent Application2,079,726, in the name of Wendel, et al. Exemplary polymer emulsions areavailable from BASF, Ludwigshafen, Germany, under the trade name AcronalDS 3446X.

The preparation of sugared starches is generally known and is described,inter alia, in Gunther Tegge, Starke und Starkederivate, Behr's Verlag,Hamburg, 1984, p. 173 and p. 220 and in EP-A 441 197. The sugaredstarches to be used according to the invention are preferably thosewhose weight average molecular weight is in the range of 4,000 to16,000, more preferably in the range from 6500 to 13000. The sugaredstarches to be used according to the invention are normally completelysoluble in water at room temperature, the solubility limit generallybeing above 50% by weight.

It is advantageous for the sugared starches to have a nonuniformity U(defined as the ratio between the weight average molecular weight M_(w)and the number average molecular weight M_(n) ; U characterizes themolecular weight distribution) in the range from 6 to 12, preferably 7to 11, more preferably 8 to 10. Additionally, it is advantageous for theproportion by weight of the sugared starches used having molecularweight of below 1000 to be at least 10% by weight, but not more than 70%by weight, preferably from 20 to 40%, based on the total weight ofstarch used.

It is advisable to use sugared starches whose dextrose equivalent DE isfrom 5 to 40, preferably from 10 to 30, more preferably from 10 to 20.The DE value characterizes the reduction capacity, relative to thereduction capacity of anhydrous dextrose, and is determined inaccordance with DIN 10308, Edition 5.71, produced by the GermanStandards Committee on Foodstuffs and Agricultural products.Furthermore, it is preferable to use sugared starches whose 40% strengthby weight aqueous solutions nave a dynamic viscosity determined inaccordance with DIN 53 019 at 25° C. and a shear gradient of 75reciprocal seconds, of from 0.01 to 0.06, preferably from 0.015 to 0.04,more preferably from 0.02 to 0.035.

It should be noted that molecular weight data reported herein forsugared starches to be used according to the invention are based ondeterminations by means of gel permeation chromatography, carried outunder the following conditions:

Columns: 3 steel units measuring 7.5×600 mm, filled with TSK gel G 2000PW; G 3000 PW and G 4000 PW. Mesh 5 microns.

Eluent: Distilled water

Temp.: Room Temperature

Detection: Differential refractometer (for example ERC 7511)

Injection Volume: 20 microliter, valve (for example VICI 6-way valve)

Evaluation: Bruker Chromstat GPC software

Calibration: The calibration was carried out in the low-molecular-weightrange using glucose, raffinose, maltose and maltopentose. For thehigher-molecular-weight range, pululan standard having a polydispersityof <1.2 was used.

The starting starches for the preparation of the sugared starches can inprinciple be any native starches, such as cereal starches, for example,corn, wheat, rice or barley, tuber and root starches, for examplepotatoes, tapioca roots or arrow root, or sago starches.

The sugared starches can be used without any further chemicalmodification, apart from the extremely simple partial hydrolysis of thestarting starch for their preparation. However, it is of course alsopossible to use them in chemically modified form, for example byetherification or esterification. This chemical modification may alsohave been carried out in advance on the starting starch beforedegradation. Esterifications are possible using both inorganic andorganic acids, or anhydrides or chlorides thereof. Phosphated andacetylated degraded starches are of particular interest. The most commonmethod of etherification is treatment with organohalogen compounds,epoxides or sulfates in aqueous alkaline solution. Particularly suitableethers are alkyl ether, hydroxyalkyl ethers, carboxyalkyl ethers andallylethers. It is also possible to use products of the reaction with2,3-epoxypropyltrimethylammonium chloride. Chemically unmodified sugaredstarched are preferred.

Suitable monomers which can be polymerized by means of free radicalsinclude monoethylenically unsaturated monomers, such as olefins, e.g.,ethylene; vinylaromatic monomers, such as styrene, α-methylstyrene,o-chlorostyrene and vinyltoluene; vinyl and vinylidene halides, such asvinyl chloride and vinylidene chloride; esters made from vinyl alcoholand monocarboxylic acids having 1 to 18 carbon atoms, such as vinylacetate, vinyl propionate, vinyl n-butyrate, vinyl laurate and vinylstearate; and esters made from α,β,-monoethylenically unsaturatedmono-and dicarboxylic acids, preferably having 3 to 6 carbon atoms, suchas acrylic acid, methacrylic acid, maleic acid, fumaric acid anditaconic acid, with alkanols generally having from 1 to 12, preferably 1to 8, more preferably 1 to 4, carbon atoms, such as ethyl, n-butyl,isobutyl and 2-ethylhexyl acrylates and methacrylates, dimethyl maleateand n-butyl maleate. The monomers are essentially insoluble in theaqueous media and generally form the principle monomers, which normallymake up a proportion of greater than 50% by weight, based on the totalamount of monomers to be polymerized.

Monomers which usually give homopolymers of increased water solubilitywhen polymerized alone are normally only copolymerized as modifyingmonomers in amounts of less than 50% by weight, in general from 0.5 to20% by weight, preferably from 1 to 10% by weight, based on the totalamount of monomers to be polymerized. Examples of such monomers areα,β-monoethylenically unsaturated mono- and dicarboxylic acids having 3to 6 carbon atoms, and amides thereof, eg. acrylic acid, methacrylicacid, maleic acid, fumaric acid, itaconic acid, acrylamide andmethacrylamide, furthermore vinylsulfonic acid and water-soluble saltsthereof, N-vinyl formamide and N-vinyl pyrrolidone. Monomers whichusually increase the internal strength of films formed by the aqueouspolymer dispersion are generally likewise only copolymerizable in minoramounts, usually from 0.5 to 10% by weight, based on the total amount ofmonomers to be polymerized. Such monomers normally contain an epoxide,hydroxyl, N-methylol or carbonyl group or a least two non-conjugatedethylenically unsaturated double bonds. In addition to monomerscontaining unsaturated double bonds, it is also possible to copolymerizeminor amounts, usually from 0.01 to 4% by weight, based on the monomersto be polymerized, of molecular weight regulators, such as tert-dodecylmercaptan. Such substances are preferably added to the polymerizationzone in a mixture with the monomers to be polymerized.

Preferred classes of aqueous polymer dispersions utilized in theadhesives according to the invention are those whose polymers areobtainable by free-radical emulsion polymerization of monomer mixtureswhich comprise from 50 to 100% by weight, based on the total weight ofmonomers to be polymerized, of monomers selected from the groupconsisting of esters of α,β-monoethylenically unsaturated carboxylicacids having from 3 to 6 carbon atoms with alkanols having 1 to 12carbon atoms, and styrene. More preferred are polymers obtainable byfree-radical emulsion polymerization of monomer mixtures which comprisefrom 90 to 99% by weight, based on the total weight of monomers to bepolymerized, of monomers selected from the group consisting of esters ofacrylic and/or methacrylic acids and alkanols having 1 to 8 carbon atomsand styrene, and 1 to 10 weight percent, based on the total weight ofmonomers to be polymerized, of monomers selected from the groupconsisting of α,β-monoethylenically unsaturated mono- and dicarboxylicacids having 3 to 6 carbon atoms, and amides thereof, preferably acrylicand methacrylic acids and amides thereof.

The aqueous polymer dispersions utilized in the inventive laminatingadhesives are preferably prepared by polymerizing the monomers by thefree-radical aqueous emulsion polymerization process in the presence ofthe sugared starches to be used in accordance with this invention. Theemulsion polymerization temperature is generally from 30 to 95° C.,preferably from 75 to 90° C. The polymerization medium may eithercomprise water alone or a mixture of water and water-miscible liquids,such as methanol. It is preferred to use water alone. The emulsionpolymerization can be carried out either as a batch process or in theform of a feed process, including a step or gradient procedure.Preference is given to the feed process, in which part of thepolymerization batch is heated to the polymerization temperature andpartially polymerized, and the remainder of the polymerization batch issubsequently fed to the polymerization zone continuously, in steps orwith superposition of a concentration gradient, usually via a pluralityof spatially separate feed streams, of which one or more contain themonomers in pure or emulsified form, while maintaining thepolymerization. Advantageously, the initially introduced mixture and/orthe monomer feed stream contains small amounts of emulsifiers, generallyless than 0.5% by weight, based on the total amount of monomers to bepolymerized, in order to reduce the surface tension of the dispersionmedium and thus to simplify stirring. The monomers are thereforefrequently fed to the polymerization zone after pre-emulsification withthese assistant emulsifiers. Due to the high water solubility of thesugared starches to be used, the feed processes can be designed in aparticularly simple manner by initially introducing all of the sugaredstarch to be used in dissolved form in an aqueous mixture; pregelling isunnecessary. This means that the aqueous solution produced on partialhydrolysis of the starting starch can, after the hydrolysis has beenterminated, for example by neutralization of the catalytic acid andcooling, be further used directly for the aqueous emulsionpolymerization. Prior isolation, for example by spray drying, of thesugared starch is unnecessary.

Suitable free-radical polymerization initiators are all those which arecapable of initiating a free-radical aqueous emulsion polymerization.These may be either peroxides, for example alkali metal peroxydisulfatesor H₂ O₂, or azo compounds.

Also suitable are combined systems comprising at least one organicreducing agent and at least one peroxide and/or hydroperoxide, e.g.,tert-butyl hydroperoxide and the sodium metal salt ofhydroxymethanesulfinic acid or hydrogen peroxide and ascorbic acid. Alsosuitable are combined systems additionally containing a small amount ofa metal compound which is soluble in the polymerization medium and whosemetallic component can exist in more than one oxidation state, whereascorbic acid is also frequently replaced by the sodium metal salt ofhydroxymethanesulfinic acid, sodium sulfite, sodium hydrogen sulfite orsodium metal bisulfite and hydrogen peroxide is frequently replaced bytert-butyl hydroperoxide or alkali metal peroxydisulfates and/orammonium peroxydisulfates. In general, the amount of free-radicalinitiator systems employed is from 0.1 to 2% by weight, based on thetotal amount of the monomers to be polymerized. Particularly preferredinitiators are ammonium and/or alkali metal peroxydisulfates, alone oras a constituent of combined systems. Particularly preferred are sodiumperoxydisulfates.

Particularly preferred polymer dispersions are obtainable byfree-radical aqueous polymerization of monomer mixtures comprising from40 to 85% by weight of at least one ester of α,β-monoethylenicallyunsaturated mono-and dicarboxylic acids having from 3 to 6 carbon atomswith alkanols having 1 to 6 carbon atoms, from 15 to 60% by weight ofstyrene, and from 1 to 10% by weight of one or more monomers selectedfrom the group consisting of α,β-monoethylenically unsaturatedcarboxylic acids having 3 to 6 carbon atoms. The dispersions contain,based on the weight of polymerized monomers, from 1 to 120% by weight,preferably from 10 to 65% by weight, of at least one added sugaredstarch. Most preferred are polymer dispersions prepared by free-radicalemulsion polymerization of monomer mixtures comprising from 74 to 84% byweight of butyl acrylate, 15 to 20% by weight of styrene and 1 to 10% byweight of acrylic acid, and from 15 to 55% by weight, of at least oneadded starch, all weights based on the total amount of monomers to bepolymerized.

The polymer dispersions prepared via free-radical emulsionpolymerization may be incorporated into the inventive adhesives withoutfurther treatment. Alternately, the polymer dispersion prepared viafree-radical emulsion polymerization may be converted to a redispersiblepowder by methods known to one skilled in the art, such as spray drying,roll drying or suction-filter drying. The powder then may be redispersedin water to form a polymer dispersion for incorporation into theinventive adhesives. Preferably the total solids content of the polymerdispersion will be from 10 to 75% by weight, more preferably from 40 to60% by weight, based on the total weight of the polymer dispersion.

The laminating adhesive compositions may further comprise a plasticizerto modify the flexibility of the dried adhesive film. In fact, whenrequired, higher levels of plasticizer may be incorporated into theinventive adhesive composition without detrimentally affecting the waterredispersibility of the dried adhesive film, when compared to adhesivescurrently being used in similar applications. Accordingly, one wouldhave more freedom in formulating laminating adhesives as claimed hereinwith respect to both acceptable film flexibility and waterredispersibility. Representative plasticizers include acetyl tributylcitrate, butyl benzyl phthalate, butyl phthalyl butyl glycolate, dibutylphthalate, dibutyl sebacate, diethyl phthalate, diethylene glycoldibenzoate, dipropylene glycol, dipropylene glycol dibenzoate, ethylphthalyl ethyl glycolate, ethyl-p-toluene sulfonamide, hexylene glycol,methyl phthalyl ethyl glycolate, polyoxyethylene aryl ester,tributoxyethyl phthalate, triethylene glycol polyester of benzoic acidand phthalic acid, or mixtures thereof. Of these plasticizers,dibenzoate types are preferred. One particular plasticizer which may beused is available from Velsicol Chemical Corporation, Rosemont, Ill.,under the trade name Benzoflex®50. While the adhesive composition neednot include any plasticizer, the plasticizer is generally used inamounts of 2 to 30 weight percent, preferably 5 to 20 weight percent,based on the total weight of the adhesive composition.

Other additives traditionally used in laminating adhesives may also beutilized herein in conventional amounts. Such additives includedefoamers, preservatives, rheology modifiers such as thickeners ordiluents, fillers, tackifiers, colorants such as dyes or pigments, andthe like. Suitable rheology modifiers include, for example, starch,oliginates, bentonite, casein, fumed silica, guar gum, xanthan gum, gumtragacanth, polyvinyl alcohol, hydroxyethylcellulose, locust bean gum,methylcellulose, and the like. One preferred rheology modifier isavailable from Alco Chemical Corporation, Chattanooga, Tenn., under thetrade name Alcogum®296W. Useful fillers include, for example, bentonite,calcium carbonate, calcium silicate, clay, mica, silica, talc, and thelike. One suitable defoamer is available from Henkel Corporation,Kankakee, Ill., under the trade name Foamaster B. A suitablepreservative is available from Merck & Company, Inc., Rahway, N.J.,under the trade name Tektamer 38 A.D.

In certain embodiments it may be desirable to add to the adhesive asurfactant at conventional levels. The surfactant can be anionic,cationic, amphoteric or nonionic surface-active compounds or mixturesthereof. Suitable anionic emulsifiers include, for example, alkylsulfonates, alkylaryl sulfonates, alkyl sulfates, sulfates ofhydroxyalkanols, alkyl and alkylaryl disulfonates, and the like.Suitable cationic emulsifiers include, for example, alkyl quaternaryammonium salts and alkyl quaternary phosphonium salts. Examples ofsuitable nonionic emulsifiers are the addition products of 5 to 50 molesof ethylene oxide adducted to straight-chain and branched-chain alkanolswith 6 to 22 carbon atoms, or alkylphenols, and the like.

,The novel water-borne laminating adhesives are used in the constructionof articles wherein a first, nonwoven substrate is bonded to a secondsubstrate. The second substrate may be another nonwoven substrate whichis compositionally the same as or different from the first nonwovensubstrate, a woven substrate, or a sheet of a thermoplastic resinprepared by methods known to those skilled in the art, such asextrusion, lamination and the like. The second substrate may be eitherwater permeable or water impermeable, depending on the particularapplication. The first nonwoven and second substrates may be preparedfrom natural or synthetic polymeric materials. Natural polymericsubstrates include, without limitation, cellulosic substrates preparedfrom, for example, wood pulp (such as paper) and cotton fibers (such ascloth, sheeting and industrial fabric). Synthetic polymeric substratesinclude, without limitation, polyester or polyolefin substrates preparedfrom, for example, polyethylene and polypropylene. In addition, otherbiodegradable polymeric materials such as polyvinyl alcohol, polyhydroxyvalerate butyrate and polylactides may be used.

The articles may include an absorbent core portion. The absorbent coreportion may comprise naturally occurring polymeric material, such ascellulosic absorbent material, i.e., wood pulp and/or paper, or highperformance superabsorbent synthetic polymeric materials, such aspolyacrylates, methacrylic acid and alkyl esters of acrylic andmethacrylic acids. The absorbent core portion may be in the form of asheet or may comprise particulate absorbent material, wherein theparticles of absorbent material are adhered together by the inventivelaminating adhesives. The absorbent core portion may comprise the firstnonwoven substrate, in which case it is bonded to the second substratewith the inventive adhesives. Preferably, the absorbent core portion isdisposed between and proximate the first nonwoven substrate and thesecond substrate and may be bonded to either the first nonwovensubstrate or the second substrate.

Typical articles utilizing the novel laminating adhesives include,without limitation, household wipes, surgical drapes, medical dressings,disposable diapers, adult incontinent products, tampons and sanitarynapkins. The use of the novel adhesives is particularly advantageous innonwoven/nonwoven, (i.e., tissue/tissue) bonding of flushable paperproducts, such as toilet tissue, and disposable diapers, where watersensitivity at relatively low temperature is desirable so as to providerelease from the various substrates to facilitate flushability of all ora portion of the diaper.

The adhesive can be applied to either the nonwoven substrate or to thesecond substrate by a variety of methods in an amount sufficient tocause the substrates to adhere one to the other. Conventional methods ofapplying the adhesives to the substrates are generally known or readilyavailable to one skilled in the art and include, for example, spraycoating, roll coating, extrusion coating, laminating, dipping, and thelike.

The following examples, which in no way are intended to limit the scopeof the claims appended hereto, illustrate the production and performanceof suitable water-borne, water redispersible laminating adhesives. Inthe examples, all parts are by weight and all temperatures in degreeCelsius unless otherwise noted.

Adhesive Formulation EXAMPLE 1

Inventive adhesive composition Example 1 was prepared by blendingtogether 82.4% of Acronal 3446 polymer dispersion (50% solids), 15% ofBenzoflex 50 plasticizer,2% of Alcogum296 W thickener,0.17% Foamaster Bdefoamer and0.46% Tektamer38 A.D. preservative.

EXAMPLE 2

Comparative adhesive composition Example 2 was prepared by blendingtogether 53.79% of a polyvinyl alcohol-modified polyvinyl acetatepolymer dispersion (50% solids) with 32.15% of water, 10.75% ofBenzoflex 50, 2.68% of polyvinyl alcohol, 0.13% of Foamaster B and 0.5%of Tektamer 38 A.D.

EXAMPLE 3

Inventive adhesive Example 3 comprises 100% of Acronal 3446 polymerdispersion (50% solids).

EXAMPLE 4

Comparative adhesive composition Example 4 was prepared by blendingtogether 60.16% of a polyvinyl alcohol-modified polyvinyl acetatepolymer dispersion (50% solids) with 36.13% of water, 3.00% polyvinylalcohol, 0.14% of Foamaster B and 0.58% of Tektamer 38 A.D.

The Examples were tested for water redispersibility and subjectiveadhesion according to the procedures set forth below.

Test Procedures Subjective Adhesion

A first nonwoven (tissue) substrate was bonded to a second nonwoven(tissue) substrate using the adhesives of Examples 1 and 2,respectively. Additionally, a first nonwoven substrate (spun-boundpolypropylene) was bonded to a second textured polypropylene filmsubstrate which had been treated to impart a degree of hydrophilicitythereto. The bonded substrates were allowed to dry thoroughly at ambientconditions. The bonded, dried substrates then were subjectivelyevaluated by physically pulling the substrates apart and noting the easeof separation of the bonded substrates.

In each case, the respective substrates bonded with the inventiveadhesive Example 1 exhibited greater adhesion, i.e., were more difficultto separate, than those substrates bonded with comparative adhesiveExample 2.

Water Redispersibility

Duplicate wet samples of the adhesive to be tested were coated ontorelease paper with a 3.0 mil bird applicator and dried overnight at roomtemperature. The samples were removed and accurately weighed. A 60 meshscreen was cut into 3 inch×3 inch squares and the squares were alsoaccurately weighed.

The adhesive Examples 1-4 were placed in an Osterizer® blender with 350ml of water at temperatures of 10° C. and 70° C., respectively.Additionally, the adhesive Example 2 was tested at 27° C. in the samemanner. A few drops of defoamer were added. The cover was placed on theblender and the blender run for 10 minutes at high speed.

Following the high speed agitation, the water dispersion and anyremaining lumps of adhesive were decanted from the blender, through the60 mesh screen, into a beaker. The lumps of adhesive remained on thescreen, while the dispersed materials flowed through the 60 mesh screen.A wash bottle was used to rinse the inside of the blender to remove anyremaining pieces of adhesive.

The screen containing any remaining adhesive was placed in an oven (49°C.) overnight. The screen was removed from the oven, allowed to cool andagain accurately weighed. The percentage of adhesive dispersed wascalculated based on the initial weight of adhesive and final weight ofthe adhesive retained on the 60 mesh screen as follows:

% redispersed adhesive=(i-f)/i×100

i=initial dry weight of adhesive applied

f=dry weight of adhesive retained on 60 mesh screen

At 10° C., the % redispersed adhesive for Examples 1-4 was 99.3, 93.4,97.6 and 97.2, respectively. At 27° C., the % redispersed adhesive forExample 2 was 82.4. At 70° C., the % redispersed adhesive for Examples1-4 was 94.1, 47.7, 99.8 and 93.3, respectively. The results clearlyindicate that the inclusion of plasticizer in the vinyl acetate-basedadhesive at significant levels, for example 10% based on total weight ofthe adhesive, detrimentally affects the water redispersibility of theadhesive as the temperature of the aqueous media is increased. The waterredispersibility of inventive adhesive Example 1 and Examples 3 and 4(0%plasticizer) were unaffected by the increase in temperature. Therefore,at temperatures where water redispersibility is essential, for examplegreater than about 15° C., the inventive adhesives clearly show improvedwater redispersibility in the presence of plasticizers.

We claim:
 1. A water-borne, water redispersible laminating adhesive comprising,an aqueous polymer dispersion prepared by radical-initiated emulsion polymerization of a mixture of unsaturated monomers in the presence of starch degradation products having a weight average molecular weight range of from 2500 to 25,000 and which are obtainable by hydrolysis in an aqueous phase; and 2 to 30 weight percent of a plasticizer, wherein the adhesive exhibits water redispersibility of greater than about 90 percent at a water-temperature of greater than about 15° C.
 2. A water-borne, water redispersible laminating adhesive comprising,an aqueous polymer dispersion prepared by radical-initiated emulsion polymerization of a mixture of unsaturated monomers in the presence of starch degradation products having a weight average molecular weight range of from 2500 to 25,000 and which are obtainable by hydrolysis in an aqueous phase; and 2 to 30 weight percent of a plasticizer selected from the group consisting of acetyl tributyl citrate, butyl benzyl phthalate, butyl phthalyl butyl glycolate, dibutyl phthalate, dibutyl sebacate, diethyl phthalate, diethylene glycol dibenzoate, dipropylene glycol, dipropylene glycol dibenzoate, ethyl phthalyl ethyl glycolate, ethyl-p-toluene sulfonamide, hexylene glycol, methyl phthalyl ethyl glycolate, polyoxyethylene aryl ester, tributoxyethyl phthalate, triethylene glycol polyester of benzoic acid and phthalic acid.
 3. The adhesive of claim 1 or 2 wherein the mixture of unsaturated monomer is selected from the group consisting of olefins, vinylaromatic monomers, esters made from vinyl alcohol and monocarboxylic acids having 1 to 18 carbon atoms, and esters made from α,β-monoethylenically unsaturated mono- and dicarboxylic acids having 3 to 6 carbon atoms and alkanols having 1 to 12 carbon atoms, and wherein the degraded starch products are present in amounts from 1 to 120% by weight, based on the total weight of monomers to be polymerized.
 4. The adhesive of claim 3 wherein the mixture of unsaturated monomers comprises from 50 to 100% by weight, based on the total weight of the monomers to be polymerized, of monomers selected from the group consisting of esters of acrylic acid and/or methacrylic acid with alkanols having 1 to 12 carbon atoms, and styrene.
 5. The adhesive of claim 4 wherein the monomer mixture comprises from 90 to 99% by weight, based on the total weight of monomers to be polymerized, of monomers selected from the group consisting of esters of acrylic and/or methacrylic acids and alkanols having 1 to 8 carbon atoms, and styrene; and 1 to 10 weight percent, based on the total weight of monomers to be polymerized, of monomers selected from the group consisting of acrylic and methacrylic acids.
 6. The adhesive of claim 3 wherein the monomer mixture comprises from 40 to 85% by weight of at least one ester of α,β-monoethylenically unsaturated mono- and dicarboxylic acids having from 3 to 6 carbon atoms with alkanols having 1 to 6 carbon atoms, from 15 to 60% by weight of styrene; and from 1 to 10% by weight of one or more monomers selected from the group consisting of α,β-monoethylenically unsaturated monocarboxylic acids having 3 to 6 carbon atoms and amides thereof, and wherein the degraded starch products are present in amounts from 10 to 65% by weight, all weights based on the total weight of monomers to be polymerized.
 7. The adhesive of claim 6 wherein the monomer mixture comprises from 74 to 84% by weight of butyl acrylate, 15 to 20% by weight of styrene; and 1 to 10% by weight of acrylic acid, and wherein the degraded starch products are present in amounts of from 20 to 55% by weight, all weights based on the total weight of monomers to be polymerized.
 8. The adhesive of claim 3 wherein the starch degradation product has a nonuniformity (U) in the range of from 6 to
 12. 9. The adhesive of claim 8 wherein at least 10% by weight, but not more than 70% by weight, of the starch degradation product has a molecular weight of less than 1,000.
 10. The adhesive of claim 9 wherein the starch degradation product has a dextrose equivalent (DE) of from 5 to
 40. 11. The adhesive of claim 9 wherein the monomer mixture comprises from 40 to 85% by weight of at least one ester of α,β-monoethylenically unsaturated mono- and dicarboxylic acids having from 3 to 6 carbon atoms with alkanols having 1 to 6 carbon atoms, from 15 to 60% by weight of styrene; and from 1 to 10% by weight of one or more monomers selected from the group consisting of α,β-monoethylenically unsaturated monocarboxylic acids having 3 to 6 carbon atoms and amides thereof, and wherein the degraded starch products are present in amounts from 10 to 65% by weight, all weights based on the total weight of monomers to be polymerized.
 12. The adhesive of claim 11 wherein the monomer mixture comprises from 74 to 84% by weight of butyl acrylate, 15 to 20% by weight of styrene; and 1 to 10% by weight of acrylic acid, and wherein the degraded starch products are present in amounts of from 20 to 55% by weight, all weights based on the total weight of monomers to be polymerized.
 13. The adhesive of claim 12 further comprising a rheology modifier. 